CancellationTokenSource.Cancel Method

Definition

传达取消请求。Communicates a request for cancellation.

Overloads

Cancel()

传达取消请求。Communicates a request for cancellation.

Cancel(Boolean)

如果出现异常,传达取消请求,并指定是否应处理其余回调和可取消操作。Communicates a request for cancellation, and specifies whether remaining callbacks and cancelable operations should be processed if an exception occurs.

Cancel()

传达取消请求。Communicates a request for cancellation.

public:
 void Cancel();
public void Cancel ();
member this.Cancel : unit -> unit
Public Sub Cancel ()

Exceptions

CancellationTokenSource 已被释放。This CancellationTokenSource has been disposed.

聚合异常包含由相关联的 CancellationToken 上已注册的回调引发的所有异常。An aggregate exception containing all the exceptions thrown by the registered callbacks on the associated CancellationToken.

Examples

下面的示例使用随机数生成器来模拟数据收集应用程序,该应用程序从第11个不同乐器读取10个整数值。The following example uses a random number generator to emulate a data collection application that reads 10 integral values from eleven different instruments. 如果值为零,则指示度量值对一个检测失败,在这种情况下,应取消该操作,而不应计算整体平均值。A value of zero indicates that the measurement has failed for one instrument, in which case the operation should be cancelled and no overall mean should be computed.

为了处理操作的可能取消,此示例实例化一个 CancellationTokenSource 对象,该对象将生成一个传递到 TaskFactory 对象的取消标记。To handle the possible cancellation of the operation, the example instantiates a CancellationTokenSource object that generates a cancellation token which is passed to a TaskFactory object. TaskFactory 对象依次将取消标记传递给负责收集特定检测的读取的每个任务。The TaskFactory object in turn passes the cancellation token to each of the tasks responsible for collecting readings for a particular instrument. 调用 TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken) 方法,以确保仅在成功收集所有读数后计算平均值。The TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken) method is called to ensure that the mean is computed only after all readings have been gathered successfully. 如果任务未被取消,则对 TaskFactory.ContinueWhenAll 方法的调用将引发异常。If a task has not because it has been cancelled, the call to the TaskFactory.ContinueWhenAll method throws an exception.

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      // Define the cancellation token.
      CancellationTokenSource source = new CancellationTokenSource();
      CancellationToken token = source.Token;

      Random rnd = new Random();
      Object lockObj = new Object();
      
      List<Task<int[]>> tasks = new List<Task<int[]>>();
      TaskFactory factory = new TaskFactory(token);
      for (int taskCtr = 0; taskCtr <= 10; taskCtr++) {
         int iteration = taskCtr + 1;
         tasks.Add(factory.StartNew( () => {
                                       int value;
                                       int[] values = new int[10];
                                       for (int ctr = 1; ctr <= 10; ctr++) {
                                          lock (lockObj) {
                                             value = rnd.Next(0,101);
                                          }
                                          if (value == 0) { 
                                             source.Cancel();
                                             Console.WriteLine("Cancelling at task {0}", iteration);
                                             break;
                                          }   
                                          values[ctr-1] = value; 
                                       }
                                       return values;
                                    }, token));   
      }
      try {
         Task<double> fTask = factory.ContinueWhenAll(tasks.ToArray(), 
                                                      (results) => {
                                                         Console.WriteLine("Calculating overall mean...");
                                                         long sum = 0;
                                                         int n = 0; 
                                                         foreach (var t in results) {
                                                            foreach (var r in t.Result) {
                                                                  sum += r;
                                                                  n++;
                                                               }
                                                         }
                                                         return sum/(double) n;
                                                      } , token);
         Console.WriteLine("The mean is {0}.", fTask.Result);
      }   
      catch (AggregateException ae) {
         foreach (Exception e in ae.InnerExceptions) {
            if (e is TaskCanceledException)
               Console.WriteLine("Unable to compute mean: {0}", 
                                 ((TaskCanceledException) e).Message);
            else
               Console.WriteLine("Exception: " + e.GetType().Name);
         }
      }
      finally {
         source.Dispose();
      }
   }
}
// Repeated execution of the example produces output like the following:
//       Cancelling at task 5
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 10
//       Unable to compute mean: A task was canceled.
//       
//       Calculating overall mean...
//       The mean is 5.29545454545455.
//       
//       Cancelling at task 4
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 5
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 6
//       Unable to compute mean: A task was canceled.
//       
//       Calculating overall mean...
//       The mean is 4.97363636363636.
//       
//       Cancelling at task 4
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 5
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 4
//       Unable to compute mean: A task was canceled.
//       
//       Calculating overall mean...
//       The mean is 4.86545454545455.
Imports System.Collections.Generic
Imports System.Threading
Imports System.Threading.Tasks

Module Example
   Public Sub Main()
      ' Define the cancellation token.
      Dim source As New CancellationTokenSource()
      Dim token As CancellationToken = source.Token

      Dim lockObj As New Object()
      Dim rnd As New Random

      Dim tasks As New List(Of Task(Of Integer()))
      Dim factory As New TaskFactory(token)
      For taskCtr As Integer = 0 To 10
         Dim iteration As Integer = taskCtr + 1
         tasks.Add(factory.StartNew(Function()
                                       Dim value, values(9) As Integer
                                       For ctr As Integer = 1 To 10
                                          SyncLock lockObj
                                             value = rnd.Next(0,101)
                                          End SyncLock
                                          If value = 0 Then 
                                             source.Cancel
                                             Console.WriteLine("Cancelling at task {0}", iteration)
                                             Exit For
                                          End If   
                                          values(ctr-1) = value 
                                       Next
                                       Return values
                                    End Function, token))   
         
      Next
      Try
         Dim fTask As Task(Of Double) = factory.ContinueWhenAll(tasks.ToArray(), 
                                                         Function(results)
                                                            Console.WriteLine("Calculating overall mean...")
                                                            Dim sum As Long
                                                            Dim n As Integer 
                                                            For Each t In results
                                                               For Each r In t.Result
                                                                  sum += r
                                                                  n+= 1
                                                               Next
                                                            Next
                                                            Return sum/n
                                                         End Function, token)
         Console.WriteLine("The mean is {0}.", fTask.Result)
      Catch ae As AggregateException
         For Each e In ae.InnerExceptions
            If TypeOf e Is TaskCanceledException
               Console.WriteLine("Unable to compute mean: {0}", 
                                 CType(e, TaskCanceledException).Message)
            Else
               Console.WriteLine("Exception: " + e.GetType().Name)
            End If   
         Next
      Finally
         source.Dispose()
      End Try                                                          
   End Sub
End Module
' Repeated execution of the example produces output like the following:
'       Cancelling at task 5
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 10
'       Unable to compute mean: A task was canceled.
'       
'       Calculating overall mean...
'       The mean is 5.29545454545455.
'       
'       Cancelling at task 4
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 5
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 6
'       Unable to compute mean: A task was canceled.
'       
'       Calculating overall mean...
'       The mean is 4.97363636363636.
'       
'       Cancelling at task 4
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 5
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 4
'       Unable to compute mean: A task was canceled.
'       
'       Calculating overall mean...
'       The mean is 4.86545454545455.

Remarks

关联的 CancellationToken 将收到取消通知,并将转换为 IsCancellationRequested 返回 true 的状态。The associated CancellationToken will be notified of the cancellation and will transition to a state where IsCancellationRequested returns true.

将执行注册到 CancellationToken 的任何回调或可取消操作。Any callbacks or cancelable operations registered with the CancellationToken will be executed.

建议将可取消操作和回调注册到 CancellationToken 不会引发异常。We recommend that cancelable operations and callbacks registered with CancellationToken not throw exceptions.

此 Cancel 重载将聚合引发到 AggregateException中的任何异常,从而引发异常的一个回调不会阻止执行其他已注册的回调。This overload of Cancel will aggregate any exceptions thrown into an AggregateException, such that one callback throwing an exception will not prevent other registered callbacks from being executed.

See also

Cancel(Boolean)

如果出现异常,传达取消请求,并指定是否应处理其余回调和可取消操作。Communicates a request for cancellation, and specifies whether remaining callbacks and cancelable operations should be processed if an exception occurs.

public:
 void Cancel(bool throwOnFirstException);
public void Cancel (bool throwOnFirstException);
member this.Cancel : bool -> unit
Public Sub Cancel (throwOnFirstException As Boolean)

Parameters

throwOnFirstException
Boolean

如果异常应立即传播,则为 true;否则为 falsetrue if exceptions should immediately propagate; otherwise, false.

Exceptions

CancellationTokenSource 已被释放。This CancellationTokenSource has been disposed.

聚合异常包含由相关联的 CancellationToken 上已注册的回调引发的所有异常。An aggregate exception containing all the exceptions thrown by the registered callbacks on the associated CancellationToken.

Remarks

关联的 CancellationToken 将收到取消通知,并将转换为 IsCancellationRequested 返回 true的状态。The associated CancellationToken will be notified of the cancellation and will transition to a state where IsCancellationRequested returns true.

将执行注册到 CancellationToken 的任何回调或可取消操作。Any callbacks or cancelable operations registered with the CancellationToken will be executed. 回调会按后进先出的顺序执行。Callbacks will be executed synchronously in LIFO order.

建议将可取消操作和回调注册到 CancellationToken 不会引发异常。We recommend that cancelable operations and callbacks registered with CancellationToken not throw exceptions.

如果 true``throwOnFirstException,则异常将立即传播到 Cancel的调用,从而阻止处理其余回调和可取消操作。If throwOnFirstException is true, an exception will immediately propagate out of the call to Cancel, preventing the remaining callbacks and cancelable operations from being processed.

如果 false``throwOnFirstException,此重载将聚合引发到 AggregateException的任何异常,从而引发异常的一个回调不会阻止执行其他已注册的回调。If throwOnFirstException is false, this overload will aggregate any exceptions thrown into an AggregateException, such that one callback throwing an exception will not prevent other registered callbacks from being executed.

See also

Applies to